How can a pacemaker (permanent artificial cardiac pacemaker) contribute to a low ejection fraction (EF)?

How Pacemakers Can Cause Low Ejection Fraction

Chronic right ventricular (RV) pacing is known to be deleterious by inducing left ventricular dyssynchrony, leading to a reduction in left ventricular ejection fraction, stroke volume, impaired LV filling, and an increased incidence of heart failure and atrial fibrillation. 1

Mechanism of Pacemaker-Induced Low EF

Right ventricular pacing creates an abnormal ventricular activation pattern similar to left bundle branch block (LBBB), which can lead to:

1. Ventricular Dyssynchrony

   • RV pacing causes the septum to contract early while delaying lateral wall contraction
   • This dyssynchronous contraction reduces pumping efficiency
   • Intra- and interventricular dyssynchrony both contribute to reduced cardiac output 2

2. Structural Remodeling

   • Long-term RV pacing leads to:
     • Inhomogeneous thickening of ventricular myocardium
     • Myofibrillar disarray
     • Increased fibrosis
     • Disturbances in ion-handling protein expression 3

3. Functional Consequences

   • Increased left ventricular end-systolic and end-diastolic volumes
   • Reduced ejection fraction
   • Impaired LV filling
   • Mitral regurgitation may develop 3
   • Shortening of filling time and prolongation of isovolumic contraction time 2

Risk Factors for Developing Low EF with Pacemakers

Not all patients with pacemakers develop reduced EF. Key risk factors include:

• Pacing burden: Higher percentage of ventricular pacing correlates with greater risk
• Pacing site: RV apical pacing is more likely to cause problems than alternative sites
• Pre-existing cardiac conditions: Patients with baseline cardiac dysfunction are more vulnerable
• Duration of pacing: Longer duration increases risk of adverse remodeling

Clinical Evidence

Studies have demonstrated that:

• Patients who mostly need atrial pacing with rare RV pacing typically have no alterations in systolic and diastolic function 1
• Upgrading from conventional RV pacing to biventricular pacing in patients who developed heart failure has shown significant improvements in EF (from 39% to 46% in one study) 2
• The BLOCK-HF study demonstrated that biventricular pacing significantly reduces adverse outcomes compared to RV pacing in patients with AV block and LV dysfunction 1

Prevention and Management

For patients requiring pacemakers who are at risk of developing low EF:

1. Minimize RV pacing when possible:

   • Program longer AV delays to encourage intrinsic conduction
   • Use algorithms designed to reduce unnecessary ventricular pacing

2. Consider alternative pacing strategies for high-risk patients:

   • Biventricular pacing (CRT) should be considered in patients with NYHA class III or IV symptoms with EF ≤35%, irrespective of QRS duration 1
   • His bundle pacing or left bundle branch area pacing may preserve more physiologic activation 4

3. For patients who develop pacing-induced cardiomyopathy:

   • Upgrade to biventricular pacing (CRT) can reverse remodeling and improve EF 2
   • Optimization of medical therapy for heart failure

Important Caveats

• The accuracy of standard echocardiographic measures (including mitral annular velocities and E/e' ratio) is reduced in patients with left bundle branch block, RV pacing, or those who have received cardiac resynchronization therapy 1
• When upgrading to biventricular pacing, there is a higher rate of complications compared to conventional pacing, primarily related to LV lead placement issues 1
• Tachycardia-induced cardiomyopathy from rapid pacing rates must be distinguished from dyssynchrony-induced cardiomyopathy, as the management differs 1

Early recognition of pacing-induced reduction in EF is essential to prevent irreversible cardiac remodeling and progressive heart failure.